PWS Conversion piston rifle close up
A few years ago when a few HK416 uppers were released to the general public there was a big surge of interest in gas piston AR’s and the perceived advantages over Direct Impingement (DI) guns. There were few options available if you wanted a gas piston rifle or upper that would work with a standard AR lower.
I became more interested after taking a Larry Vickers class when he described the development history of the HK416 and his involvement with it. He also had good things to say about the LWRC series of gas piston uppers and rifles. Unfortunately, LWRC was still having quality control issues and HK416 uppers were running in the neighborhood of $5K so availability was limited.
I stumbled across the
Primary Weapons System Gas Piston Conversion when I was shopping online for one of their DNTC compensators. The big advantage of the PWS system to me was that they would install their piston kit on the customer’s existing upper. Since I had a few components already laying around such as a Colt 1/9 heavy barrel, upper receiver and bolt carrier group this seemed like a logical choice to get in to piston AR’s. I was also able to take advantage of their Military/Law Enforcement discount to reduce the cost further.
PWS Gas Block and Centurion Arms HK style Front Sight
I sent in my components after placing an order through the PWS site and received my upper back a few weeks later. I had ordered the PWS FSC556 compensator along with a barrel threading service as well as the Daniel Defense 9.5 FSP Lite rail. My initial trip to the range proved to be a disappointment with the upper short stroking every other round. I tried several different brands of ammo which worked with my other AR. Same results even after using different magazines as well as swapping lower receivers. I contacted Todd at PWS and explained what happened, he seemed surprised as they do a test fire on each upper before it leaves using Wolf (normally underpowered) ammo. I believed him since the shell deflector on the upper had some wear marks which weren’t there when I sent the parts in. He asked that I send it back to PWS so they could investigate the cause of failure.
After I got it back from PWS I took it out to the range and fired about 200 rounds to zero and function test it since I had planned on taking it to a carbine instructor class with Bennie Cooley. It worked well and my confidence was restored in the weapon. PWS stated that they opened up the gas port slightly to fix it.
I took it to the Bennie Cooley carbine course in August 2008 and ran it for the first half of the day before I started having malfunctions again. Same symptoms, it would fire one or two rounds before having a failure to extract. I switched rifles so that I could complete the training day before attempting to troubleshoot it later that night. The only thing that I could see was that it appeared that the gas block was slightly loose, enough that you could see a small bit of a gap between the block and the barrel. I tried shooting it the next day with no improvement and sent it back to PWS after the course.
Surefire 6P with clickie tailcap and shock isolated bezel in a Larue LT606 offset mount
After speaking with several people at PWS I asked that they turn down the barrel from the HBAR profile to a mid-weight profile as the combined weight of the gas block, flashlight and barrel made it very muzzle heavy. They charged me about $125 for that but later offered to have the gas piston assembly Ion-Bonded for me at no charge if I was willing to wait an extra few weeks. I agreed since it seemed like a fair deal. As far as the malfunctions I was experiencing, PWS explained that some of the factory barrels from Colt had an almost undetectable taper where the front sight base was mounted and that could cause gas leakage.
I took it out to the range again and fired another 200 rounds to confirm zero and experienced no malfunctions. More recently I switched out the Aimpoint M2 with an Eotech 552 in a Larue mount and found that the HK style diopter sights sit too low with the Larue riser and I cannot align the iron sights through the Eotech window. I still don’t have enough rounds through it to feel 100% confident but I have been very impressed with the professionalism and customer service from the PWS staff, they even sent me a free hat the last time I had the upper sent in.
A friend shooting the PWS AR with Eotech mounted on Larue LT-110 riser
Since the whole premise of having a piston AR is increased reliability I see no advantage to my current PWS set up over my conventional DI carbines. I like the DD 9.5 FSP rail as I’m able to get my support hand farther out on the gun but the PWS gas block vents in that area which makes it extremely hot. I normally wear gloves but even then I can feel the rails getting hot. Rail covers help and I’ve switched to Magpul XT panels since they seem to offer the best balance of texture and heat shielding compared to the ladder style rail covers included with the Daniel Defense rail.
The HK style sights have been disappointing, the front sight post is fixed and too wide to make any sort of precision shot even at 50 yards to zero. The rear diopter is too small to effectively shoot in any form of low light, you will need a white light to backlight the front sight post in order to get a clear sight picture.
Having briefly experimented with running different collapsible stocks including the Magpul MOE and Vltor Modstock, I found that because of the increased weight toward the muzzle the only stock that can counter balance that is the LMT SOPMOD buttstock. It is also the most comfortable (and expensive) of all the options.
I have been impressed with the PWS FSC556 compensator, coupled with the piston drive and increased muzzle weight there is almost no muzzle rise even when shooting rapid fire.
The VTAC padded sling is attached to the rail using a Midwest Industries QD socket on the left side of the rail closest to the upper receiver. I find that location allows me to run my support hand out and activate the Surefire without interfering with the sling attachment.
The grip is an Ergo ambidextrous SureGrip which fits my hand perfectly but still allows me to activate the ambi-safety without shifting my firing grip.
I have a few carbine classes scheduled before the end of the year and plan on giving the system a more thorough evaluation.
